1. Field of the Invention
This invention relates generally to densitometers and, more particularly, to an improved method and apparatus for graphically displaying densitometer output information under microprocessor control so as to eliminate the need for optically scanning the sample to be analyzed a second time.
2. Statement of the Prior Art
Densitometers are well-known as devices which scan a sample and provide an output signal or graphical display indicative of the optical density, transmittance, absorption or the like of the scanned sample.
One well-known use of the densitometer is to scan a sample of blood which has been prepared by the electrophoresis process. Electrophoresis of blood samples isolates various proteins in the blood, known as albumin, alpha-1 globulin, alpha-2 globulin, beta-globulin and gamma-globulin. The electrophoresis technique separates these proteins from each other and then the sample may be processed or scanned in a densitometer. Each of the proteins exhibits a different light absorption characteristic or pattern and the light absorption patterns are graphically displayed by the densitometer to indicate the presence and quantity of each of these proteins.
In optical density analysis, the amount of light passing through the sample is an inverse logarithmic function of the optical density of the sample. Thus, if the optical density of the sample is doubled, the transmitted light is reduced by a factor of ten. The light transmitted through a sample falls on a photo-responsive element which generates electrical signals having a current proportional to the amount of transmitted light. The current output of the photo-responsive element is, therefore, also a logarithmic function of the optical density which then is converted into analog or time-varying signals directly proportional to the optical density pattern of the scan sample. The analog signals drive a graphic display unit to provide a permanent curve or record of the optical density pattern. All this is well-known.
In addition to scanning densitometry which measures the emergent radiation passing through a sample as a measure of the sample's density either by transmittance or absorbance measurements, fluorescent densitometry is gaining wide acceptance in clinical laboratories. Some materials, when excited by energy of a short wavelength, re-emit light of a longer wavelength. The procedures presently used in laboratories fluoresce efficiently when excited by light at 366nm. The ultraviolet energy is used only to excite the fluorescent material and, unlike transmission densitometry, is not the light used for quantitation. The only light detected and measured in fluorescent densitometry is the light emitted by the sample and the relationship between the emitted light of the sample and its concentration is linear rather than logarithmic as it is with transmission densitometry. Hence, with fluorescent techniques, a linear rather than a logarithmic amplifier may be used for measurement purposes.
In either case, the electrical analog signals generated by the photo-responsive elements, when graphically displayed, exhibit a series of peaks and valleys. In the analysis of blood, the area under the optical density curve and bounded by the two adjacent valleys separated by one peak, is representative of the quantity of each protein in the sample and is referred to as a sample fraction. The important data is the relative percentage of each protein and the selection of these fraction boundaries, i.e., the precise locations of these valleys is somewhat arbitrary and results in inaccurate analysis of the blood sample. The problem is not unique to evaluation of blood samples, but is common to optical and magnetic density valuations and, in fact, to all evaluations of analog data.
There are various prior art systems which have considered this problem which provide a standardized graphical display of the densitometer output. For example, U.S. Pat. Nos. 3,185,820 issued May 25, 1965 to A. P. Williams, et al; 3,553,444 issued on Jan. 5, 1971to P. P. Tong; 3,706,877 issued Dec. 19, 1972 to G. F. Clifford, Jr., et al; 3,767,899 issued Oct. 23, 1973 to L. D. Barter; 3,784,789 issued on Jan. 8, 1974 to J. A. Vandenbroek; 3,842,422 issued Oct. 15, 1974 to J. A. Vandenbroek; 3,902,813 issued Sep. 2, 1975 to J. A. Vandenbroek, et al. and 4,005,434 issued on Jan. 25, 1977 to T. L. Golias, et al. disclose various systems for analyzing the densitometer output and for minimizing the problems involved. The densitometer output is graphically displayed as an analog signal or curve indicative of optical density and a second signal which is the integral of the optical density, i.e., the area under the optical density curve, and which may be either analog, or numerical or both. In each of these patents, various analog computational circuitry is employed.
There are three common techniques for determining the location of the fraction boundaries or valleys. In the first technique, the densitometer includes circuitry to automatically detect the valleys between the peaks based upon changes in the slope of the curve, integrate the area under the curve between valleys and print out the integral in numerical form. Then, in order to determine the percent of each protein, the operator of the equipment has to add the printed values to obtain a denominator and then calculate each percent by dividing each printed value by the calculated denominator.
Not only is this time consuming, but if, in fact, the computer system erroneously selected a particular boundary location, the results are useless to the physician evaluating the blood sample. Hence, the results of the computer print-out cannot conveniently be utilized for subsequent evaluation if the physician analyzing the blood sample disagrees with the particular boundary decisions made by the computer.
A second type of system provides two graphic displays, the first being the optical density of the scanned sample and the second being the integral of the optical density pattern. These are plotted or traced on graph paper and at a later time, the physician can select the particular boundaries for each protein. Then the area under the curve is calculated by actually manually counting the number of squares under the curve between each pair of boundaries which is equivalent to the aforementioned printed values. Again, the percentage of each protein is then calculated by the addition and division procedure explained previously. Again, however, this requires laborious manual counting as well as manual calculations resulting in lost time and increasing the potential for error.
Finally, the third type of system provides both of these techniques together, i.e., a numerical print-out and a curve so that the boundaries may be manually selected if the position is not satisfied with the automatically selected boundaries. However, this still does not eliminate the manual counting and addition-division procedure for obtaining percentages of each protein.
Therefore, a fourth technique has been devised as illustrated in the more recent of the above-identified patents whereby the densitometer output is graphically displayed as an analog signal or curve indicative of optical density and the computer-selected fraction boundaries are displayed as well. The operator is then allowed to inspect and edit the curve and he may add, delete or modify boundary decisions so that a second scan of the same sample will provide more accurate information. Furthermore, techniques have been developed to obtain maximum utilization of the optical density curve by determining the maximum optical density or maximum peak value of a particular sample during a first scan and then adjusting the values of the optical density curve so that the maximum value comes as near to a full scale reading as possible and is assigned a value of unity for normalizing the graphic display without distortion and thereby providing more pronounced valleys or fraction boundaries.
Additionally, systems have been evolved which normalize not only the optical density curve but also normalize the integral of the optical density pattern once the technician or physician operating the system has satisfied himself as to the location of each fraction boundary for each protein thereby eliminating the aforementioned addition, division steps and allowing direct computer evaluation.
Several of the systems of the prior art employ analog devices which utilize two separate and distinct scans of each sample with a delay between successive scans. On the first scan, the analog computer records the scanned optical density pattern by recording it on graph paper or the like and the operator is able to make all of the fraction boundary decisions based on his observation of the plotted optical density curve before he provides his information to an integrating unit which receives the electrical representations of the signal.
In such systems, the time-varying electrical input signals are provided to both the recorder and to a delay unit and the sheet of paper carrying the plot of the optical density curve is passed beneath a cursor. The distance between the printer and the cursor is sufficient to give an operator time to study the curve that emerges and make decisions relative to fraction boundaries. When a point on the curve responding to a boundary, as determined by the operator, passes under the cursor, a switch is pushed providing a signal relative to the boundary and the delayed output signal is provided to an integrator in a timed relation to the passage of the curve under the cursor so that when the button is pressed the integral count is returned to zero. Simultaneously, a second marker produces an appropriate blip on the chart paper to identify the boundaries of the fractions which are being calculated.
Since operators considered this a very demanding and tiring operation and since it is highly subject to human failure due to the time pressures put on the operator as the paper passes beneath the cursor and the time lag between the operator decision to modify a boundary and the pressing of the button to effect the change, more automatic systems have been devised whereby machine decisions are conveyed to an operator to allow the operator to modify machine decisions before the integrals are actually calculated. But even in such systems, a re-scanning of the original sample or a re-scanning of the marked up or modified graph paper is required. The room for human error is still too great and the accuracy of the results is insufficient for many purposes. A fully automatic computer system which minimizes the possibility for human error, optimizes normalization and calculation accuracy and requires only a single rather than a double scan is required.
The present invention solves substantially all of the problems of the prior art in a single system by using a microprocessor-controlled densitometer system which requires only a single optical scan of the sample being analyzed and utilizes the computation capacity of a microprocessor to insure the accuracy of numerical calculations while insuring that machine-made boundary decisions are viewed on a CRT device by the operator who then edits the displayed optical density waveform pattern to add, delete or otherwise modify boundary decisions and the like prior to the actual integrations, ratio or percentage calculations, scalings, etc., and prior to the recording of the required analog profile trace on a fixed record medium and the corresponding printed information relating thereto.